Method of forming a stacked polishing pad using laser ablation

ABSTRACT

The present invention provides a method of manufacturing a polishing pad for chemical mechanical polishing, comprising laminating a top polishing pad to a sub-polishing pad to form a stacked pad and transferring the stacked pad to a laser-ablation station containing a laser. Further the invention provides modulating a laser beam from the laser to modify both the top polishing pad and the sub-polishing pad and inspecting the laser-ablated stacked pad.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 60/718,490 filed Sep. 19, 2005.

FIELD OF THE INVENTION

The present invention relates to polishing pads used for chemical-mechanical planarization (CMP), and in particular, relates to a method of forming a stacked polishing pad using laser ablation.

BACKGROUND OF THE INVENTION

In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting, and dielectric materials are deposited on or removed from a surface of a semiconductor wafer. Thin layers of conducting, semiconducting, and dielectric materials may be deposited by a number of deposition techniques. Common deposition techniques in modern processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and electrochemical plating (ECP).

As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization. Planarizing a surface, or “polishing” a surface, is a process where material is removed from the surface of the wafer to form a generally even, planar surface. Planarization is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. Planarization is also useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide an even surface for subsequent levels of metallization and processing.

Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize substrates such as semiconductor wafers. In conventional CMP, a wafer carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate urging the wafer against the polishing pad. The pad is moved (e.g., rotated) relative to the substrate by an external driving force. Simultaneously therewith, a chemical composition (“slurry”) or other fluid medium is flowed onto the substrate and between the wafer and the polishing pad. The wafer surface is thus polished by the chemical and mechanical action of the pad surface and slurry in a manner that selectively removes material from the substrate surface.

Rutherford et al., in U.S. Pat. No. 6,007,407, discloses polishing pads for performing CMP that are formed by laminating two separate layers (“stacked pad”). The upper polishing layer is attached to a lower layer or “sub-pad” formed from a material suitable for supporting the polishing layer. The sub-pad typically has higher compressibility and lower stiffness than the polishing layer and essentially acts as supporting “cushions” for the polishing layer. Conventionally, the two layers are bonded with a pressure-sensitive adhesive (“PSA”).

Unfortunately, manufacturing of the stacked pad is somewhat cumbersome, time-consuming and cost prohibitive, as it requires numerous steps in multiple machines to form the various features of the pad. For example, the following is an overview of a typical method of forming a conventional stacked pad comprising a radial and XY groove pattern, and computer-numerical control (“CNC”) holes:

A) Radial Lathe

-   1. Machine radial grooves in top pad. -   2. Machine cut-off grooves in top pad. -   3. Inspect groove quality. -   4. Transfer pads to XY lathe.     B) XY Linear Grooves -   5. Align radial grooved pad on XY table. -   6. Machine XY groove pattern. -   7. Inspect groove quality. -   8. Transfer pads to sub pad laminating.     C) Sub Pad Lamination -   9. Laminate top polishing pad to sub-polishing pad (“stacked pad”). -   10. Align and cut stacked pad. -   11. Inspect alignment and cutting quality. -   12. Transfer stacked pad to CNC hole operation.     D) CNC Hole -   13. Align composite pad to ensure XY pattern matches hole alignment     configuration. -   14. Punch CNC holes. -   15. Inspect alignment and hole quality. -   16. Transfer pads to Final Inspection packaging and inventory     control operation.

As shown from above, the conventional method requires numerous steps and machines, requiring additional time and expense in manufacturing a stacked polishing pad. Accordingly, what is needed is a method of forming a polishing pad for chemical mechanical polishing that is less cumbersome, less time-consuming and cost effective to manufacture.

SUMMARY OF THE INVENTION

In one aspect of the invention, there is provided a method of manufacturing a polishing pad for chemical mechanical polishing, comprising: laminating a top polishing pad to a sub-polishing pad to form a stacked pad; transferring the stacked pad to a laser-ablation station containing a laser; modulating a laser beam from the laser to modify both the top polishing pad and the sub-polishing pad; and inspecting the laser-ablated stacked pad.

In another aspect of the invention, there is provided a method of manufacturing a composite polishing pad for chemical mechanical polishing, comprising: laminating a top polishing pad to a sub-polishing pad with an adhesive layer to form a stacked pad; transferring the stacked pad to a laser-ablation station containing a laser; modulating a laser beam from the laser to modify the top polishing pad, adhesive layer and the sub-polishing pad from a specific reference point; and inspecting the laser-ablated stacked pad from the specific reference point without transferring the stacked pad.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of the method of the present invention for forming a stacked pad;

FIG. 2 illustrates a flowchart providing an embodiment of the process for manufacturing the stacked pad of the present invention; and

FIG. 3 illustrates a CMP system utilizing the polishing pad of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A method for manufacturing a stacked pad utilizing pulsed laser-ablation with energy modulation and focus control is provided. The stacked pad may be mounted on a table, and the laser mounted to an XY plotter, to provide a vast combination of radial grooves, XY grooves, and holes that can be machined with a single tool. In addition, the method provides the ability to machine complex patterns (e.g., integral windows) without an alignment tool. The energy modulation and focus control allows the laser to cut or machine laminate materials of different compositions. As the laser cuts through each individual layer, the energy is modulated and the laser is focused to match the cutting requirements of the next layer in the laminate stack. Advantageously, the entire machining and final pad cutting operation can be accomplished on a single tool. In other words, the modulated pulsed laser is capable of performing all machine steps, eliminating the need for task specific machining equipment. Also, the reduction in process steps results in operation consolidation and simplification. In addition, the present invention permits additional benefits including, elimination of alignment issues between cutting and machining tools by utilizing a single tool, elimination or assistance in sub-pad edge sealing, elimination of tool wear issues, reduction of maintenance costs and spare parts and elimination of manual errors by utilizing CNC equipment.

Referring now to the drawings, FIG. 1 illustrates an exemplary method for forming the stacked pad of the present invention. In particular, a stacked polishing pad 10 is illustrated that includes a base layer 12 (“sub-polishing pad”) and an upper polishing layer 14 (“top polishing pad”). Base layer 12 can be made of, for example, polymer impregnated felt (e.g., Suba IV™ by Rohm and Haas Electronic Materials CMP Inc. of Newark, Del.) or filled polymeric sheets. Further, in an example embodiment, upper polishing layer 14 can be made of polymer impregnated felts, poromerics, filled polymer sheets (e.g., IC1000™ by Rodel, Inc. of Newark, Del.), or unfilled textured polymers.

Polishing pad 10 also includes an adhesive layer 20 that bonds base layer 12 to polishing layer 14. In an example embodiment, the adhesive layer 20 is an inexpensive and readily available, thermoplastic or thermoset material. In particular, adhesive layer 20 is a material selected from the following group of adhesives: polyolefins, ethylene vinyl acetate, polyamides, polyesters, polyurethanes, polyvinyl chloride and epoxies. In addition, adhesive layer 20 may be a pressure-sensitive adhesive. Optionally, polishing pad 10 may include an additional adhesive 22 attached to the platen-exposed end of the base layer 12.

In addition, polishing pad 10 may include an aperture with a window fixed therein (not shown). In one example embodiment, the window is permanently fixed (“integral window”) in the aperture, while in another example embodiment it is removably fixed in the aperture. The window is transparent to wavelengths of light used to perform optical in-situ measurements of a substrate (e.g., wafer W) during planarization. Example wavelengths range from 190 to 3500 nanometers.

In addition, the method of the present invention includes a laser 5 that outputs a laser beam 7 that is modulated to modify the various polishing layers of the stacked pad. In other words, the laser beam 7 can modify both the top polishing pad and the sub-polishing pad. In addition, the laser beam can modify the adhesive layer as well. Preferably, a specific reference point on the polishing pad is utilized to modify the pad. In addition, the modified pad can be inspected, utilizing the specific reference point, without transferring the stacked pad.

Note, laser 5 can be moved in any direction (i.e., x, y or z plane) to accommodate numerous designs or configurations as desired. In the present invention, any supporting member (not shown), for example, a table to support the polishing pad in a laser machining station, need not be moved relative to the laser 5. Rather, laser 5 can be moved to achieve, for example, the desired removal of a selected polishing layer or adhesive, independent of any movement of the supporting member. In addition, an inert gas may be provided from a nozzle (not shown) to reduce oxygen at the cutting surface, reducing burns or chars on the cutting surface edge. Also, the laser beam may be utilized in conjunction with a high pressure waterjet to reduce the heat that may be produced by conventional laser cutting processes. Thermal laser ablation is preferred.

In the present embodiment, the laser 5 used for micromachining may be pulsed excimer lasers that have a relatively low duty cycle, YAG or CO² lasers. Optionally, laser 5 may be a continuous laser that is shuttered (i.e., the pulse width (time) is very short compared to the time between pulses). Example lasers are MicroAblator™ from Exitech, Inc. Note, even though excimer lasers have a low average power compared to other larger lasers, the peak power of the excimer lasers can be quite large. The peak intensity and fluence of the laser is given by: Intensity (Watts/cm²)=peak power (W)/focal spot area (cm²) Fluence (Joules/cm²)=laser pulse energy (J)/focal spot area (cm²) while the peak power is: Peak power (W)=pulse energy (J)/pulse duration (sec)

During laser ablation, several key parameters should be considered. An important parameter is the selection of a wavelength with a minimum absorption depth. This should allow a high energy deposition in a small volume for rapid and complete ablation. Another parameter is short pulse duration to maximize peak power and to minimize thermal conduction to the surrounding work material. This combination will reduce the amplitude of the response. Another parameter is the pulse repetition rate. If the rate is too low, energy that was not used for ablation will leave the ablation zone allowing cooling. If the residual heat can be retained, thus limiting the time for conduction, by a rapid pulse repetition rate, the ablation will be more efficient. In addition, more of the incident energy will go toward ablation and less will be lost to the surrounding work material and the environment. Yet another important parameter is the beam quality. Beam quality is measured by the brightness (energy), the focusability, and the homogeneity. The beam energy is less useful if it can not be properly and efficiently delivered to the ablation region. Further, if the beam is not of a controlled size, the ablation region may be larger than desired with excessive slope in the sidewalls.

In addition, if the removal is by vaporization, special attention must be given to the plume. The plume will be a plasma-like substance consisting of molecular fragments, neutral particles, free electrons and ions, and chemical reaction products. The plume will be responsible for optical absorption and scattering of the incident beam; and it can condense on the surrounding work material and/or the beam delivery optics. Normally, the ablation site is cleared by a pressurized inert gas, such as nitrogen or argon.

Referring now to FIG. 2, a flow chart illustrating the method of the present invention is provided. In step S1, the top polishing pad 14 is laminated to the sub-polishing pad 12 with an adhesive 20 to form a stacked pad 10. Note, the stacked pad 10 may also include an additional adhesive 22. Next, in step S2, the stacked pad 10 is transferred to a pulsed laser machining station. In step S3, the stacked pad 10 is machined and cut utilizing a specific reference point and without transferring the pad to another station. Here, stacked pad 10 is subjected to laser ablation, under modulation and focus control, to create the various features of the stacked polishing pad. For example, the laser ablation can be utilized to create CNC holes into the stacked polishing pad. Also, the method can be utilized to groove the top polishing pad, including, a pad containing a window therein. Other features of the invention include, laser ablating different top polishing and sub-polishing pads to form a composite polishing pad, laser ablating an edge of the sub-polishing pad to seal the sub-polishing pad, laser ablating to level the polishing pad, and laser ablating to form a composite polishing pad having at least three polishing pad layers. Thermal laser ablation is preferred.

Next, in step S4, the modified stacked polishing pad 10 is inspected for any defects or flaws. Preferably, the inspection is performed without transferring the stacked polishing pad 10, utilizing the specific reference point. Thereafter, in step S5, the modified stacked polishing pad 10 is transferred to a final inspection packaging and inventory control operation.

Accordingly, the present invention provides a method of manufacturing a polishing pad for chemical mechanical polishing, comprising laminating a top polishing pad to a sub-polishing pad to form a stacked pad and transferring the stacked pad to a laser-ablation station containing a laser. Further the invention provides modulating a laser beam from the laser to modify both the top polishing pad and the sub-polishing pad and inspecting the laser-ablated stacked pad.

Referring now to FIG. 3, a CMP apparatus 20 utilizing the laser-ablated stacked polishing pad of the present invention is provided. Apparatus 20 includes a wafer carrier 22 for holding or pressing the semiconductor wafer 24 against the polishing platen 26. The polishing platen 26 is provided with a stacked polishing pad 10 of the present invention. As discussed above, pad 10 has a bottom layer 12 that interfaces with the surface of the platen 26, and a top polishing pad 14 that is used in conjunction with a chemical polishing slurry to polish the wafer 24. Note, although not pictured, any means for providing a polishing fluid or slurry can be utilized with the present apparatus. The platen 26 is usually rotated about its central axis 27. In addition, the wafer carrier is usually rotated about its central axis 28, and translated across the surface of the platen 26 via a translation arm 30. Note, although a single wafer carrier is shown in FIG. 3, CMP apparatuses may have more than one spaced circumferentially around the polishing platen. In addition, a transparent hole 32 is provided in the platen 26 and overlies the window 4 of the stacked pad 10. Accordingly, transparent hole 32 provides access to the surface of the wafer 24, via the window 4, during polishing of the wafer 24 for accurate end-point detection. Namely, a laser spectrophotometer 34 is provided below the platen 26 that projects a laser beam 36 to pass and return through the transparent hole 32 and window 4 for accurate end-point detection during polishing of the wafer 24. 

1. A method of manufacturing a polishing pad for chemical mechanical polishing, comprising: laminating a top polishing pad to a sub-polishing pad to form a stacked pad; transferring the stacked pad to a laser-ablation station containing a laser; modulating a laser beam from the laser to modify both the top polishing pad and the sub-polishing pad; and inspecting the laser-ablated stacked pad.
 2. The method of claim 1 further comprising laser ablating CNC holes into the polishing pads.
 3. The method of claim 1 further comprising grooving the top polishing pad, the pad containing a window therein.
 4. The method of claim 1 further comprising laser ablating different top polishing and sub-polishing pads to form a composite polishing pad.
 5. The method of claim 1 further comprising laser ablating an edge of the sub-polishing pad to seal the sub-polishing pad.
 6. The method of claim 1 further comprising leveling the polishing pad.
 7. A method of manufacturing a composite polishing pad for chemical mechanical polishing, comprising: laminating a top polishing pad to a sub-polishing pad with an adhesive layer to form a stacked pad; transferring the stacked pad to a laser-ablation station containing a laser; modulating a laser beam from the laser to modify the top polishing pad, adhesive layer and the sub-polishing pad from a specific reference point; and inspecting the laser-ablated stacked pad from the specific reference point without transferring the stacked pad.
 8. The method of claim 7 further comprising laser ablating CNC holes into the polishing pads.
 9. The method of claim 7 further comprising laser ablating an edge of the sub-polishing pad to seal the sub-polishing pad.
 10. The method of claim 7 further comprising laser ablating at least another adhesive layer in the polishing pad. 